# std::stof, std::stod, std::stold

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< cpp‎ | string‎ | basic string

Defined in header `<string>` |  |
float stof ( const std::string& str, std::size_t* pos = nullptr ); | (1) | (since C++11)
float stof ( const std::wstring& str, std::size_t* pos = nullptr ); | (2) | (since C++11)
double stod ( const std::string& str, std::size_t* pos = nullptr ); | (3) | (since C++11)
double stod ( const std::wstring& str, std::size_t* pos = nullptr ); | (4) | (since C++11)
long double stold( const std::string& str, std::size_t* pos = nullptr ); | (5) | (since C++11)
long double stold( const std::wstring& str, std::size_t* pos = nullptr ); | (6) | (since C++11)

Interprets a floating point value in a string str.

Let ptr be an internal (to the conversion functions) pointer of type char* (1,3,5) or wchar_t* (2,4,6), accordingly.

1) Calls std::strtof(str.c_str(), &ptr).
2) Calls std::wcstof(str.c_str(), &ptr).
3) Calls std::strtod(str.c_str(), &ptr).
4) Calls std::wcstod(str.c_str(), &ptr).
5) Calls std::strtold(str.c_str(), &ptr).
6) Calls std::wcstold(str.c_str(), &ptr).

Function discards any whitespace characters (as determined by std::isspace) until first non-whitespace character is found. Then it takes as many characters as possible to form a valid floating-point representation and converts them to a floating-point value. The valid floating-point value can be one of the following:

- decimal floating-point expression. It consists of the following parts:

  - (optional) plus or minus sign
  - nonempty sequence of decimal digits optionally containing decimal-point character (as determined by the current C locale) (defines significand)
  - (optional) `e` or `E` followed with optional minus or plus sign and nonempty sequence of decimal digits (defines exponent to base 10)

- hexadecimal floating-point expression. It consists of the following parts:

  - (optional) plus or minus sign
  - `0x` or `0X`
  - nonempty sequence of hexadecimal digits optionally containing a decimal-point character (as determined by the current C locale) (defines significand)
  - (optional) `p` or `P` followed with optional minus or plus sign and nonempty sequence of decimal digits (defines exponent to base 2)

- infinity expression. It consists of the following parts:

  - (optional) plus or minus sign
  - `INF` or `INFINITY` ignoring case

- not-a-number expression. It consists of the following parts:

  - (optional) plus or minus sign
  - `NAN` or `NAN(`char_sequence`)` ignoring case of the `NAN` part. char_sequence can only contain digits, Latin letters, and underscores. The result is a quiet NaN floating-point value.

- any other expression that may be accepted by the currently installed C locale

If pos is not a null pointer, then ptr will receive the address of the first unconverted character in str.c_str(), and the index of that character will be calculated and stored in *pos, giving the number of characters that were processed by the conversion.

### Parameters

str | - | the string to convert
pos | - | address of an integer to store the number of characters processed

### Return value

The string converted to the specified floating point type.

### Exceptions

std::invalid_argument if no conversion could be performed.

std::out_of_range if the converted value would fall out of the range of the result type or if the underlying function (std::strtof, std::strtod or std::strtold) sets errno to ERANGE.

### Example

| This section is incomplete Reason: no example

### Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR | Applied to | Behavior as published | Correct behavior
--- | --- | --- | ---
LWG 2009 | C++11 | std::out_of_range would not be thrown if the converted value would fall out of the range of the result type | will throw
LWG 2403 | C++11 | `stof` called std::strtod or std::wcstod | `stof` calls std::strtof or std::wcstof

### See also

stoistolstoll (C++11)(C++11)(C++11) | converts a string to a signed integer (function)
stoulstoull (C++11)(C++11) | converts a string to an unsigned integer (function)
from_chars (C++17) | converts a character sequence to an integer or floating-point value (function)

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